The present invention relates generally to a system and method for wireless communications and more particularly to a method for wireless digital communications between multiple nodes located at a distance from each other.
In wireless communication, devices send and receive messages (data flows) through radio or other means without being physically connected. Wireless devices may include portable computers, cellular telephones, personal digital assistants (PDAs), communications equipment, location sensors and the like. Mobile processing devices with wireless communication capability can be coupled to a computer network, such as the Internet or the World Wide Web. The IEEE 802.11 standards (including IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, and IEEE 802.11n) include known techniques for coupling wireless devices (which might be mobile stations) to a computer network. In the IEEE 802.11 standard, wireless devices seek out and select “access points” (herein sometimes called “AP's”). Each wireless device associates itself with a particular AP, with which it communicates. Each mobile station determines from time to time if it has good communication with its associated AP, and whether it would have better communication with a different AP. As a result of this determination, mobile stations may associate with another AP.
Access points exhibit a known deficiency when servicing data flows from different mobile stations. Because multiple devices may operation on a given frequency, data collisions occur when two or more mobile stations attempt to transmit at the same time. Accordingly, wireless standards have collision avoidance and correction mechanisms to reduce the negative impact of data collisions and to recover from them when they occur. Generally, the collision avoidance systems involve a random delay time such that each station waits a random amount of time before attempting to transmit. In most cases, this allows for one station to transmit first and not collide with the other station. In wireless networks covering a wide area, collision avoidance systems are less affective because each mobile station may be too far away from neighboring mobile stations to sense when the neighboring station is transmitting. Therefore, when two or more mobile stations transmit they are unaware of the other station's transmissions and will not effectuate collision avoidance procedures.
Additionally, because the IEEE 802.11 standards require backward compatibility, differing wireless devices may be connected to the access points using different transmission speeds. Consequently slower devices require more “air time” to transmit the same amount of information as compared to newer, higher bandwidth devices. Since air time, by necessity, must be shared among the differing wireless devices that utilize the same access point, a slower wireless device causes a general slowdown for other devices operating with the access point. This slowdown adversely impacts systems where the quality of service (QoS) is important such as digital voice systems. In digital voice systems, transmission latency may provide a degradation of service that is apparent to a listener.